This invention relates to a novel process for desalination employing ion exchange resins having both weakly acidic groups and weakly basic groups, wherein the weakly basic groups are converted to a carbonate form and the resin is thermally regenerated, consequently allowing the resin to retain a high capacity for desalination.
In desalination using ion-exchange resins having both weakly acidic groups and weakly basic groups, a heat-regeneration type desalination process is known whereby cyclic use of the resin is accomplished by eluting and regenerating the resin by application of heat. The desalination capacity obtainable by this process is low, e.g., about 0.1 gram equivalent per liter of resin beads.
The most widely adopted ion-exchange method for desalination has been chemical regeneration which uses two kinds of ion-exchange resins, i.e., cation-exchange resins and anion-exchange resins, and which accomplishes cyclic use of these resins by regenerating the resins by an acid regenerant and a base regenerant, respectively. The effective desalination capacity obtained by this process is high, being about 0.4 to 0.8 gram equivalent per liter of the combined volume of the two kinds of resins.
To achieve the same level of desalination the conventional thermal regeneration type desalination process must therefore use a volume of ion-exchange resin several times the volume used by ordinary chemical regeneration type desalination processes. The thermal regeneration process, accordingly, requires more space for equipment and larger regin inventories which require a larger amount of heat for equivalent desalination.